1. Technical Field
The invention relates to the conversion of data from one format to another format. More particularly, the invention relates to the conversion of interleaved data to a planar data format, for example the conversion of interleaved CMYK image data to planar image data.
2. Description of the Prior Art
Color separation is used, for example, in color printing where each of three colors (i.e. cyan, magenta, yellow) and black are printed from separate print heads. Each print head receives data from a separate portion of the printer memory, such that four copies of an image are retained in memory. That is, a separate copy of the image to be printed is retained in memory for each color, where each copy contains only the information necessary to print a particular layer of the image. This technique is referred to as CMYK or planar printing because each color layer comprises a separate plane of the resultant image.
Color separation can also be effected by generating a word of data for each pixel in the image, where such data word contains all four layers of color information for that pixel. This technique is referred to as interleaved printing because each color layer is interleaved with each other color layer to produce a word of composite color information for each pixel.
Either of the above approaches produces data that correspond to a color image and that can be stored in a memory.
Often color images are input pixel by pixel, i.e. interleaved. That is, when an image is scanned, all the information for each pixel is scanned simultaneously because the scanner physically sees one pixel first and then the next pixel in sequential order. Thus, there is a physical motivation for using the interleaved format.
On the other hand, an obvious way of storing an image for multi-pass printing is by separating the different colors over four different color planes, e.g. cyan, magenta, yellow, and black. For example, a color laser printer prints in multiple passes, where there is a printing pass for each color plane. Thus, the printer may print a first pass in cyan. It prints a next pass in magenta, and then in yellow.
Thus, it can be seen that a scanner often produces image information in an interleaved format, while a four-pass laser printer prefers such information in a planar format.
Accordingly, in such devices as color copiers, which comprise both a color scanner for capturing a color image and a color printer for recording the image on paper, there is a need for efficiently and quickly converting from an interleaved format to a planar format. It is therefore desirable to provide a technique to process the two four-color data formats, while meeting the format needs of various input and output devices, where such input and output devices use some combination of these two formats.
One way of performing such conversion is to provide additional storage space, i.e. more memory, where an adequate buffer is available for each plane. Thus, the interleaved data are readily sorted in sequential order, for example in an interleaved CMYK color system, to four separate buffers, where there is one buffer for each color plane. While this approach is simple, a system having 128 MB total RAM storage capacity in which an image requires 117 MB of such storage, does not provide sufficient capacity to perform the foregoing calculation. The cost and space required to add additional memory for such calculation, e.g. an additional 117 MB of RAM, makes the implementation of such simple scheme prohibitively expensive.
It would be advantageous to provide a scheme that allows for data format conversion, e.g. between an interleaved data format and a planar data format, without significantly increasing the form factor, processor speed, or RAM memory requirements of the target device, e.g. a color copier or color laser printer.